The activated carbon product SediMite™ used in the technology for reducing legacy contaminants known as PCBs in DNREC’s A-Street Ditch cleanup pilot project in Wilmington.
A new report prepared for the Delaware Department of Natural Resources and Environmental Control indicates that the innovative technology being tested in Wilmington’s A-Street Ditch cleanup pilot project continues to perform against a major legacy contaminant in a Delaware waterway. The report summarizes data collected two years after biologically treated carbon pellets were applied to sediments in the ditch to clean up polychlorinated biphenyls (PCBs).
Conducted by the DNREC’s Watershed Approach to Toxics Assessment and Restoration (WATAR) program, the technology deployed in the A-Street Ditch project uses an activated carbon product (SediMite™) with the addition of PCB-destroying micro-organisms. The activated carbon sequesters PCBs and over time the micro-organisms degrade and destroy the PCBs.
PCBs are persistent, bioaccumulative and toxic legacy industrial compounds. They pose ecological and human health risks, and are the largest contributor to fish consumption advisories issued by DNREC and the Delaware Division of Public Health.
Results of DNREC’s July 2021 sampling in the A-Street Ditch showed that total PCB concentrations in surface sediments have decreased approximately 50% across the project area. The result indicates that the microorganisms added to the carbon pellets are performing as expected. Concentrations of dissolved PCBs in the sediment porewater – the water trapped between grains of sediment in the bottom of a body of water – showed a slight increase across the project area since the 2020 monitoring, but are still 32% less than baseline conditions measured in 2019. This indicates that the carbon continues to sequester PCBs, thus reducing ecological risk. DNREC plans to assess PCB concentrations in sediment, surface water and sediment porewater one final time in July 2022.
Other A-Street ditch PCB data collected in 2021 indicates that the anomalous results received from a sediment sample collected in 2020 were likely due to inadvertent sampling of deeper, more contaminated sediments. The overall data showing the slight increase in 2021 surface water and sediment porewater PCB concentrations is likely due to ongoing impacts from within the watershed. Although not a surprise to DNREC scientists, this finding highlights the importance of cleaning up land-based sources of contamination before performing larger-scale sediment remediation and in-water restoration activities.
DNREC’s A-Street Ditch pilot project was supported by Hazardous Substance Cleanup Act (HSCA) funds and a U.S. Environmental Protection Agency multi-purpose grant. Visit the DNREC-WATAR webpage for monitoring reports and a DNREC YouTube video about the A-Street Ditch project. Visit the DNREC-CBR4 webpage to find out more about what DNREC is doing to help clean up the lower Christina and Brandywine Rivers.
The Delaware Department of Natural Resources and Environmental Control protects and manages the state’s natural resources, protects public health, provides outdoor recreational opportunities and educates Delawareans about the environment. The DNREC Division of Watershed Stewardship develops and implements innovative watershed assessment, monitoring and implementation activities. For more information, visit the website and connect with @DelawareDNREC on Facebook, Twitter or LinkedIn.